Presently, more and more attentions are paid on oxide TFT, which uses an oxide semiconductor layer as an active layer. The oxide TFT has advantages of high carrier mobility, low cost and compatible with the existing α-Si TFT production line.
Hereinafter, several typical structures of the conventional oxide TFT are described.
FIG. 1 is a structural schematic view of a conventional oxide TFT. As shown in FIG. 1, the conventional oxide TFT comprises: a substrate 110; a gate electrode 120 formed on the substrate; an insulation layer 130 covering the gate electrode 120; an active layer 140 formed on the insulation layer 130; a source electrode 151 and a drain electrode 152 formed on both sides of the active layer 140; and a passivation layer 160 covering the active layer 140 as well as the source electrode 151 and the drain electrode 152. Disadvantages of this TFT structure are in that: etching damages occur on the surface of the active layer 140 in the process of forming the source electrode 151 and the drain electrode 152 so that the electrical performance of the TFT decreases, and the active layer will be subjected to other damages in subsequent processes because its surface is exposed.
FIG. 2 is a structural schematic view of another conventional oxide TFT. As shown in FIG. 2, this conventional oxide TFT comprises: a substrate 210; a gate electrode 220 formed on the substrate 210; an insulation layer 230 covering the gate electrode 220; an active layer 240 formed on the insulation layer 230; an etching barrier layer 250 provided on the active layer 240; a source electrode 261 and a drain electrode 262 provided on both sides of the active layer 240 and the etching barrier layer 250; and a passivation layer 270 provided in the topmost layer and covering the whole device. Unlike the structure of the TFT shown in FIG. 1, the TFT shown in FIG. 2 has the etching barrier layer 250. The function of the etching barrier layer is: preventing the surface of the active layer 240 from being etch-damaged in the process of forming the source electrode 261 and the drain electrode 262. Disadvantage of this TFT structure are in that: the surface of the active layer 240 may subject to plasma bombardment in the process of forming the etching barrier layer 250 so that the electrical performance of the active layer 240 may be degraded. Further, because the etching barrier layer is provided on the active layer, there exists a problem of providing an additional mask for the etching barrier layer.
FIG. 3 is a structural schematic view of another conventional oxide TFT. As shown in FIG. 3, the conventional oxide TFT comprises: a substrate 310, a gate electrode 320, an insulation layer 330, an active layer 340, a barrier layer 350, via holes 351 and 352, a source electrode 361, a drain electrode 362, and a passivation layer 370. Disadvantages of this TFT structure are in that: the active layer 340 still subjects to damages when forming the barrier layer 350 although the barrier layer 350 provides a certain protection for the active layer, and an additional mask is also needed to form the via holes 351 and 352.
FIG. 4 is a structural schematic view of another conventional oxide TFT. As shown in FIG. 4, a gate electrode 320′ and a gate insulation layer 330′ are formed on a substrate 310′ in this order. Then, a source electrode 341′ and a drain electrode 342′ are formed, and finally an active layer 350′ is formed. This structure can avoid the etch damages to the active layer. However, because the active layer is exposed, the damages to the active layer in the subsequent processes can not be avoided.